The fate of Giardia and Cryptosporidium in marine water

Abstract

The fate and occurrence of Giardia and Cryptosporidium were studied in the marine environment to assess their potential for transmission since their transmission to swimmers in fresh waters has been previously documented. The first part of this study was designed to determine the occurrence of Giardia and Cryptosporidium at bathing beaches within the vicinity of an outfall discharging primary treated sewage into Mamala Bay, Hawaii. Sites were monitored monthly and quarterly for parasites by passing 400 liters of marine water through a spun polyproplyene fiber filter. Giardia and Cryptosporidium were detected in primary treated sewage from the Sand Island sewage treatment plant which discharges into Mamala Bay at concentrations of 2,560 cysts and 216 oocysts/liter, respectively. Ala Wai Canal as well as the bathing beaches within the vicinity of the outfall were also found to contain the parasites. The survival of Giardia in marine water was studied in direct sunlight and the dark in marine waters (33- to 35-ppt salinity), canal water (28-ppt salinity) and in phosphate-buffered saline (8-ppt) at 18 to 28°C. Giardia muris was inactivated by 3-logs in the presence of sunlight in marine and canal waters. In comparison, Giardia survive up to 6 hours in PBS under the same conditions. Overall, it appears that salinity and sunlight quickly inactivate Giardia cysts. Thus, Giardia would pose a threat only if the cysts reach the bathing beaches within a few hours. The last phase of this project was designed to develop a more efficient method of collection of cysts and oocysts from water. Methods for the concentration of enteric viruses, Giardia and Cryptosporidium from water requires the use of two different types of filters. This study compared the efficiency of their concentration from tap water and tertiary treated wastewater with a polypropylene fiber cartridge, and the Filterite electronegative and the 1MDS Virosorb electropositive microporous filters. Results indicated that the overall efficiency was greatest for the Filterite filter for both Giardia and Cryptosporidium (p = 0.000762 and p = 0.067069, respectively); and in addition they are easier and faster to process than the polypropylene-wound parasite filter.